The present invention in the field of solid state digital test and debugging instrumentation relates more particularly to a handheld voltage indicating test probe for current mode logic circuitry.
In the prior art visually indicating handheld test probes have been developed and adapted to sense binary voltage levels. Principally circuits have been developed to sense high level voltage excursions such as those occurring in TTL digital circuitry, see for example, U.S. Pat. No. 3,838,339, issued to W. F. Brandt on Sept. 24, 1974.
In current mode logic circuitry voltage excursions between HIGH and LOW are measurable in the few hundreds of millivolts. Furthermore, it is useful in testing and debugging current mode logic circuitry to know not only whether a test point is HIGH or LOW but also whether a given logic pin is at a MIDRANGE level, OPEN (a valid input condition for CML), or at SUPPLY VOLTAGE level.